Power transmission system of hybrid electric vehicle

ABSTRACT

A power transmission system of a hybrid electric vehicle may includes an input shaft, a first planetary gear set disposed on the input shaft while including three rotation elements having a first sun gear, a first planetary carrier, and a first ring gear; a second planetary gear set having a second sun gear, a second planetary carrier, and a second ring gear; a third planetary gear set having a third sun gear, a third planetary carrier, and a third ring gear; first to seventh rotation shafts, and three friction elements configured to selectively connect the respective rotation shafts to each other or selectively connect the respective rotation shafts to the transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of KoreanPatent Application No. 10-2014-0097365 filed on Jul. 30, 2014, theentire contents of which is incorporated herein for all purposes by thisreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power transmission system of a hybridelectric vehicle, and more particularly, to a power transmission systemof a hybrid electric vehicle capable of suppressing conversion into anENG mode by providing sufficient power performance at the time of wideopen throttle (WOT) oscillation and maximally using power of an engineat the time of conversion into a first HEV mode and a third HEV mode.

2. Description of Related Art

An environmentally-friendly technology of a vehicle is a core technologywhich controls a survival of a future automobile industry and advancedcar makers have focused their own energy on the development of anenvironmentally-friendly vehicle to achieve environment and fuelefficiency regulations.

Therefore, each car maker has developed an electric vehicle (EV), ahybrid electric vehicle (HEV), a fuel cell electric vehicle (FCEV), andthe like, as a future vehicle technology.

As described above, since the future vehicle has several technicalrestrictions such as weight, cost, and the like, the car makers havepaid attention to the hybrid electric vehicle as an alternative to solverealistic problems such satisfaction of exhaust gas regulations andenhancement of fuel efficiency performance and are fiercely competing tocommercialize the hybrid electric vehicle.

The hybrid electric vehicle is a vehicle using more than two powersources and may be combined in several ways. Here, as the power source,a combination of a gasoline engine or a diesel engine using traditionalfossil fuel and a motor/generator driven by electrical energy is used.

The hybrid electric vehicle may be implemented as an EV mode driven onlyby a motor, an HEV mode simultaneously using the engine and the motor,and an ENG mode using only the engine, depending on a combination of anengine and a motor.

Further, the hybrid electric vehicle drives a power generator usingkinetic energy of a vehicle, instead of using idle stop stopping theengine at the time of stopping the vehicle and using braking by theexisting friction at the time of braking the vehicle. In this case, itis possible to more remarkably enhance fuel efficiency than the typicalvehicle due to fuel saving, and the like by regenerative braking tostore electrical energy generated by the driving of the power generatorin a battery and reuse the stored electrical energy at the time ofdriving.

As described above, a power transmission system of a hybrid electricvehicle is classified into a single mode scheme and a multi-mode scheme.

The single mode scheme may not require torque transfer mechanisms, suchas a clutch and a brake, for a shift control, but may have reducedefficiency at the time of high-speed driving and thus low fuelefficiency and require an additional torque amplifier for applying to alarge vehicle.

The multi-mode scheme may have high efficiency at the time of high-speeddriving and may be designed to amplify a torque, and as a result, may beapplied to a medium and large size vehicle.

Recently, therefore, the multi-mode scheme rather than the single modescheme has been mainly adopted and thus a study thereon has beenactively conducted.

The power transmission system based on the multi-mode scheme isconfigured to include a plurality of planetary gear sets, a plurality ofmotors/generators used as a motor and a power generator, a plurality oftorque transfer mechanisms (friction elements) which may controlrotation elements of the planetary gear set, a battery used as the powersource of the motor/generator, and the like.

The power transmission system based on the multi-mode scheme hasdifferent operation mechanisms depending on a connection configurationof the planetary gear set, the motor/generator, and the toque transfermechanism.

Further, the power transmission system based on the multi-mode scheme isdifferent in durability, power transmission efficiency, a size, and thelike depending on the connection configuration, and therefore in thefield of the power transmission system of the hybrid electric vehicle,research and development to implement more robust, compact powertransmission system without power loss has been continued.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing apower transmission system of a hybrid electric vehicle having advantagesof suppressing conversion into an ENG mode by providing sufficient powerperformance at the time of wide open throttle (WOT) oscillation andmaximally using power of an engine at the time of conversion into afirst HEV mode and a third HEV mode.

Further, various aspects of the present invention are directed toproviding a power transmission system of a hybrid electric vehiclehaving advantages of reducing an electrical load by increasing an usageof a mechanical power transmission path to use large power of an engine,reducing a mode conversion frequency by replacing an ENG mode at thetime of oscillation, and minimizing a change in a rotation speed of allthe rotation elements at the time of mode conversion.

In addition, various aspects of the present invention are directed toproviding a power transmission system of a hybrid electric vehiclehaving advantages of providing a drivable ENG mode without an electricalload of a motor/generator to enhance fuel efficiency at the time ofhigh-speed driving.

An aspect of the present invention provides a power transmission systemof a hybrid electric vehicle, including an input shaft configured to beinput with power of an engine, an output gear configured to be disposedon the input shaft without rotation interference, a first planetary gearset configured to be disposed on the input shaft while including threerotation elements configured of a first sun gear, a first planetarycarrier, and a first ring gear, a second planetary gear set configuredto be disposed on the same shaft line as the first planetary gear setwhile including three rotation elements configured of a second sun gear,a second planetary carrier, and a second ring gear, a third planetarygear set configured to be disposed on the same shaft line as the secondplanetary gear set while including three rotation elements configured ofa third sun gear, a third planetary carrier, and a third ring gear, afirst rotation shaft configured to be directly connected to a firstmotor/generator as one of the rotation elements of the first planetarygear set, a second rotation shaft configured to be directly connected tothe output gear while directly connecting one of the rotation elementsof the first planetary gear set ruled out from the rotation elementsconfiguring the first rotation shaft to one of the rotation elements ofthe second planetary gear set, a third rotation shaft configured to bedirectly connected to the input shaft as one of the rotation elements ofthe first planetary gear set ruled out from the rotation elementsconfiguring the first and second rotation shafts, a fourth rotationshaft configured to be directly connected to the second motor/generatorwhile directly connecting one of the rotation elements of the secondplanetary gear set ruled out from the rotation elements configuring thesecond rotation shaft to one of the rotation elements of the thirdplanetary gear set, a fifth rotation shaft configured to be selectivelyconnected to a transmission housing as one of the rotation elements ofthe second planetary gear set ruled out from the rotation elementsconfiguring the second and fourth rotation shafts, a sixth rotationshaft configured to be continuously connected to the transmissionhousing as one of the rotation elements of the third planetary gear setruled out from the rotation elements configuring the fourth rotationshaft, a seventh rotation shaft configured to be selectively connectedto the third rotation shaft as one of the rotation elements of the thirdplanetary gear set ruled out from the rotation elements configuring thefourth and sixth rotation shafts, and three friction elements configuredto selectively connect the respective rotation shafts to each other orselectively connect the respective rotation shafts to the transmissionhousing.

All of the first, second, and third planetary gear sets may beconfigured of a single pinion planetary gear set and may include thefirst rotation shaft configured to include the first sun gear and to bedirectly connected to the first motor/generator, the second rotationshaft configured to include the first planetary carrier and the secondplanetary carrier which are directly connected to each other and to bedirectly connected to the output gear, the third rotation shaftconfigured to include the first ring gear and to be directly connectedto the input shaft, the fourth rotation shaft configured to include thesecond sun gear and the third ring gear which are directly connected toeach other and to be directly connected to the second motor/generator,the fifth rotation shaft configured to include the second ring gear andto be selectively connected to the fourth rotation shaft or thetransmission housing, the sixth rotation shaft configured to include thethird sun gear and to be directly connected to the transmission housing,and the seventh rotation shaft configured to include the third planetarycarrier and to be selectively connected to the third rotation shaft.

The three friction elements may include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing, a first clutch configured of a direct connection means of thesecond planetary gear set and configured to selectively connect thefourth rotation shaft to the fifth rotation shaft, and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.

Further, in connection with the first and second clutches and the firstbrake, in EV mode 1, the first brake may be operated, in EV mode 2, thefirst clutch may be operated, in HEV mode 1, the first brake may beoperated, in HEV mode 2, the first clutch may be operated, in HEV mode3, the second clutch may be operated, in ENG mode 1, the first brake andthe second clutch may be operated, and in ENG mode 2, the first clutchand the second clutch may be operated.

The three friction elements may include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing, a first clutch configured of a direct connection means of thesecond planetary gear set and configured to selectively connect thesecond rotation shaft to the fifth rotation shaft, and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.

The three friction elements may include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing, a first clutch configured of a direct connection means of thesecond planetary gear set and configured to selectively connect thesecond rotation shaft to the fourth rotation shaft, and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.

The first planetary gear set may be configured of a double pinionplanetary gear set and the second and third planetary gear sets areconfigured of a single pinion planetary gear set and the first, second,and third planetary gear sets may include the first rotation shaftconfigured to include the first sun gear and to be directly connected tothe first motor/generator, the second rotation shaft configured toinclude the first ring gear and the second planetary carrier which aredirectly connected to each other and to be directly connected to theoutput gear, the third rotation shaft configured to include the firstplanetary carrier and to be directly connected to the input shaft, thefourth rotation shaft configured to include the second sun gear and thethird ring gear which are directly connected to each other and to bedirectly connected to the second motor/generator, the fifth rotationshaft configured to include the second ring gear and to be selectivelyconnected to the second rotation shaft or the transmission housing, thesixth rotation shaft configured to include the third sun gear and to bedirectly connected to the transmission housing, and the seventh rotationshaft configured to include the third planetary carrier and to beselectively connected to the third rotation shaft.

The first and third planetary gear sets may be configured of a singlepinion planetary gear set and the second planetary gear set may beconfigured of a double pinion planetary gear set and the first, second,and third planetary gear sets may include the first rotation shaftconfigured to include the first sun gear and to be directly connected tothe first motor/generator, the second rotation shaft configured toinclude the first planetary carrier and the second ring gear which aredirectly connected to each other and to be directly connected to theoutput gear, the third rotation shaft configured to include the firstring gear and to be directly connected to the input shaft, the fourthrotation shaft configured to include the second sun gear and the thirdring gear which are directly connected to each other and to be directlyconnected to the second motor/generator, the fifth rotation shaftconfigured to include the second planetary carrier and to be selectivelyconnected to the fourth rotation shaft or the transmission housing, thesixth rotation shaft configured to include the third sun gear and to bedirectly connected to the transmission housing, and the seventh rotationshaft configured to include the third planetary carrier and to beselectively connected to the third rotation shaft.

The first and second planetary gear sets may be configured of a singlepinion planetary gear set and the third planetary gear set may beconfigured of a double pinion planetary gear set and the first, second,and third planetary gear sets may include the first rotation shaftconfigured to include the first sun gear and to be directly connected tothe first motor/generator, the second rotation shaft configured toinclude the first planetary carrier and the second planetary carrierwhich are directly connected to each other and to be directly connectedto the output gear, the third rotation shaft configured to include thefirst ring gear and to be directly connected to the input shaft, thefourth rotation shaft configured to include the second sun gear and thethird planetary carrier which are directly connected to each other andto be directly connected to the second motor/generator, the fifthrotation shaft configured to include the second ring gear and to beselectively connected to the second rotation shaft or the transmissionhousing, the sixth rotation shaft configured to include the third sungear and to be directly connected to the transmission housing, and theseventh rotation shaft configured to include the third ring gear and tobe selectively connected to the third rotation shaft.

According to the exemplary embodiments of the present invention, in theoverall configuration, the two EV modes, the three HEV modes, and thetwo ENG modes may be implemented by the combination of the threeplanetary gear sets, the three friction elements, and the twomotors/generators.

Further, according to the exemplary embodiments of the presentinvention, a larger torque than an engine torque may be transmitted tothe output shaft to increase the usage of the mechanical powertransmission path and to use the larger engine power than thespecification of the same first motor/generator.

Further, according to the exemplary embodiments of the presentinvention, the larger torque than the engine torque may be transmittedto the output shaft to perform the high rotation operation with the highengine power at the same vehicle speed at the time of WOT oscillationand obtain the larger acceleration.

Further, according to the exemplary embodiment of the present invention,since in the HEV mode, the larger acceleration than the ENG mode may beobtained, a necessity of conversion into the ENG mode at the time ofoscillation is removed to configure the relatively simple system andreduce the friction element depending on the mode reduction, therebymore increasing the efficiency.

Further, it is possible to perform the driving without the electricalload of the first and second motors/generators by providing the ENG modeat the time of the high-speed driving, thereby improving the fuelefficiency.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 2 is an operation table for each operation mode of the frictionelements which are applied to the power transmission system according tothe various exemplary embodiments of the present invention.

FIG. 3 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 4 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 5 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 6 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 7 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

However, portions unrelated to the description will be omitted in orderto obviously describe exemplary embodiments of the present invention,and same or similar reference numerals will be used to describe same orsimilar components throughout the present specification.

In the following description, the reason of differentiating names ofcomponents into a first, a second, and the like is to differentiatecomponents having the same name and therefore an order thereof is notnecessarily limited thereto.

FIG. 1 is a configuration diagram of a power transmission systemaccording to a first exemplary embodiment of the present invention.

Referring to FIG. 1, a power transmission system according to anexemplary embodiment of the present invention is configured of acombination of first, second, and third planetary gear sets PG1, PG2,and PG3, first and second motors/generators MG1 and MG2, and threefriction elements CL1, CL2, and BK1.

The first planetary gear set PG1 is configured of a single pinionplanetary gear set and includes a first sun gear S1, a first ring gearR1, and a first planetary carrier PC1 which supports a first pinion P1externally meshed with the first sun gear S1 and the first ring gear R1,respectively.

The second planetary gear set PG2 is configured of the single pinionplanetary gear set and includes a second sun gear S2, a second ring gearR2, and a second planetary carrier PC2 which supports a second pinion P2externally meshed with between the second sun gear S2 and the secondring gear R2.

The third planetary gear set PG3 is configured of the single pinionplanetary gear set and includes a third sun gear S3, a third ring gearR3, and a third planetary carrier PC3 which rotatably supports a thirdpinion P3 externally meshed with between the third sun gear S3 and thethird ring gear R3.

The first, second, and third planetary gear sets PG1, PG2, and PG3 aresequentially disposed on the same shaft line from an engine (ENG) andinclude seven rotation shafts TM1 to TM7 while the respective rotationelements thereof are directly or selectively connected to each other.

In more detail, the first planetary carrier PC1 of the first planetarygear set PG1 is directly connected to the second planetary carrier PC2of the second planetary gear set PG2, the second sun gear S2 of thesecond planetary gear set PG2 is directly connected to the third ringgear R3 of the third planetary gear set PG3, and the third planetarycarrier PC3 of the third planetary gear set PG3 is selectively connectedto the first ring gear R1 of the first planetary gear set PG1, and thefirst, second, and third planetary gear sets include seven rotationshafts TM1 to TM7.

The first rotation shaft TM1 is configured of the first sun gear S1 andis directly connected to the first motor/generator MG1.

The second rotation shaft TM2 is configured to include the firstplanetary carrier PC1 and the second planetary carrier PC2 and isdirectly connected to the output gear OG, and thus is continuouslyoperated as an output element.

The third rotation shaft TM3 is configured to include the first ringgear R1 and is directly connected to the input shaft IS, and thus iscontinuously operated as the input element.

The fourth rotation shaft TM4 is configured to include the second sungear S2 and the third ring gear R3 and is directly connected to thesecond motor/generator MG2.

The fifth rotation shaft TM5 is configured to include the second ringgear R2 and is also operated as the fixed element while beingselectively connected to the fourth rotation shaft TM4 or thetransmission housing H.

The sixth rotation shaft TM6 is configured to include the third sun gearS3 and is operated as the fixed element while being connected to thetransmission housing H.

The seventh rotation shaft TM7 is configured to include the thirdplanetary carrier PC3 and is selectively connected to the third rotationshaft TM3.

The first motor/generator MG1 and the second motor/generator MG2 eachhave the motor and generator functions as an independent power source.

The first motor/generator MG1 serves as a motor which is directlyconnected to the first rotation shaft TM1 to supply rotation power orserves as a power generator which generates electricity while rotatingby a torque of the first rotation shaft TM1.

The second motor/generator MG2 serves as a motor which is directlyconnected to the fourth rotation shaft TM4 to supply rotation power orserves as a power generator which generates electricity while rotatingby a torque of the fourth rotation shaft TM4.

The first and second clutches CL1 and CL2 among the friction elementsare a friction element selectively connecting between the rotationelements and the first brake BK1 is a friction element selectivelyconnecting the rotation elements to the fixed element (transmissionhousing) and may be configured of multi-plate type hydraulic frictionelements which are friction-coupled with each other by oil pressure.

The first brake BK1 may be disposed to selectively connect the fifthrotation shaft TM5 to the transmission housing H, and thus the fifthrotation shaft TM5 may be selectively operated as the fixed element.

The first clutch CL1 interconnects two of the three rotation shafts TM2,TM4, and TM5 including three rotation elements of the second planetarygear set PG2, and thus the second planetary gear set PG2 is in a directconnection state and in FIG. 1, is disposed between the fourth rotationshaft TM4 and the fifth rotation shaft TM5, and the second clutch CL2selectively connects the third rotation shaft TM3 to the seventhrotation shaft TM7.

FIG. 1 illustrates that the input shaft IS, the third rotation shaftTM3, and the sixth rotation shaft TM6 are disposed on the same shaftline and thus the input shaft IS and the third rotation shaft TM3 areconsidered as the same shaft but the exemplary embodiment of the presentinvention is not limited thereto, and therefore the third rotation shaftTM3 and the sixth rotation shaft TM6 are set as a hollow shaft and thusmay be disposed at an outer circumferential portion of the input shaftIS without rotation interference.

Further, FIG. 1 illustrates that the engine ENG is disposed in front ofthe first planetary gear set PG1 but the exemplary embodiment of thepresent invention is not limited thereto, and therefore the engine ENGmay be disposed in back of the third planetary gear set PG3.

FIG. 2 is an operation table for each operation mode of the frictionelements which are applied to the planetary gear train according to thefirst exemplary embodiment of the present invention.

Referring to FIG. 2, an operation state of the friction elements foreach operation mode will be described below.

In EV mode 1, the first brake BK1 is operated, in EV mode 2, the firstclutch CL1 is operated, in HEV mode 1, the first brake BK1 is operated,in HEV mode 2, the first clutch CL1 is operated, in HEV mode 3, thesecond clutch CL2 is operated, in ENG mode 1, the first brake BK1 andthe second clutch CL2 are operated, and in ENG mode 2, the first andsecond clutches CL1 and CL2 are operated.

As described above, the power transmission system according to the firstexemplary embodiment of the present invention may implement two EVmodes, three hybrid driving modes, and two ENG modes.

Hereinafter, an operation principle for each mode will be describedbelow.

[EV Mode 1]

The EV mode is a mode which supplies power of the battery to themotor/generator in the state in which the engine stops to drive thevehicle with the power of the motor/generator.

The EV mode may have a large effect on enhancement of fuel efficiencysince the engine stops and perform reverse driving without a separatereverse apparatus and is operated at the time of starting and low-speeddriving after stopping and requires a deceleration shift ratio whichmakes a power source more rapidly rotate than an output member forpreventing a vehicle from sliding back on an uphill road or rapidacceleration of the vehicle.

Under the condition, in the EV mode 1, the operation of the secondmotor/generator MG2 is controlled in the state in which the fifthrotation shaft TM5 is operated as the fixed element by the operation ofthe first brake BK1 to perform a deceleration output depending on a gearratio of the second planetary gear set PG2 while performing an input tothe fourth rotation shaft TM4.

[EV Mode 2]

The motor/generator has efficiency which is changed depending on arotation speed and a torque, which device that a conversion ratio intomechanical energy of the rotation and the torque among electrical energyeven though the same current is supplied is different.

That is, a current of the battery used in the EV mode is energyaccumulated by combustion of fuel in the engine or regenerative brakingand efficiently using the accumulated energy independent of thegenerated path is directly connected with the enhancement of fuelefficiency.

For this reason, recently, the electric vehicle is inclined to have atransmission of at least two stages and even in the EV mode, the hybridelectric vehicle preferably has a transmission of at least two stages,and therefore even in the exemplary embodiment of the present invention,the hybrid electric vehicle is considered to have the EV mode 2.

In consideration of this aspect, describing the shift process of the EVmode 2, in the EV mode 2, a vehicle speed is increased during thedriving in the EV mode 1 and thus the operation of the first brake BK1is released at the place where the efficiency of the secondmotor/generator MG2 is poor and the operation of the first clutch CL1 iscontrolled.

Then, the first clutch CL1 which is the direct connection device of thesecond planetary gear set PG2 is operated and therefore the secondplanetary gear set PG2 is in a direct connection state, such that allthe rotation shafts TM2, TM4, and TM5 provide an output as an inputwhile rotating at the same speed.

[HEV Mode 1]

In the HEV mode 1, the power of the engine is transmitted to the outputmember through a mechanical path and an electrical path, and the powerdistribution is performed by the planetary gear set, and the engine andthe motor/generator connected to the planetary gear set may arbitrarilycontrol the rotation speed independent of the vehicle speed andtherefore may serve as an electronically controlled continuouslyvariable transmission.

Therefore, the typical transmission has a fixed engine speed and torquewith respect to the given vehicle speed, while the electronicallycontrolled continuously variable transmission may freely change theengine speed and the torque, thereby maximizing the operation efficiencyof the engine and enhancing the fuel efficiency.

In consideration of this aspect, in the EV mode 1, the second rotationshaft TM2 of the first planetary gear set PG1 is restricted by beingconnected to the output gear OG and the rest first and third rotationshafts TM1 and TM3 freely rotate.

Therefore, after the engine (ENG) starts using the first motor/generatorMG1, the speed of the engine ENG and the first motor/generator MG1 maybe controlled independent of the vehicle speed.

[HEV Mode 2]

According to the exemplary embodiment of the present invention, an inputbranch mode may be set into two, a rotation speed ratio of the engineand the motor/generator with respect to the vehicle speed may begenerally set into two by changing the gear ratio of the secondplanetary gear set PG2, and a level of the rotation speed with respectto each rotation element is reduced as a whole, thereby helping enhancethe fuel efficiency.

In the EV mode 2, only the second rotation shaft TM2 of the firstplanetary gear set PG1 is restricted by being connected to the outputgear OG and the rest first and third rotation shafts TM1 and TM3 freelyrotate.

Therefore, when the engine ENG and the first motor/generator MG1 arecontrolled, the speed of the engine ENG and the first motor/generatorMG1 may be controlled in a continuously variable way independent of thevehicle speed.

Further, when the first motor/generator MG1 rotates counterclockwise,the first motor/generator MG1 serves as the generator and when the firstmotor/generator MG1 rotates clockwise (in this case, the engine ENG hasa more reduced rotation speed than before), the first motor/generatorMG1 serves as the motor.

As such, since the engine ENG and the first motor/generator MG1 may becontrolled in the continuously variable way if necessary, it is possibleto exhibit excellent performance in the fuel efficiency and the powerperformance.

[HEV Mode 3]

In an HEV input branch mode, the rotation speed of the motor/generatorconnected to the output member is restricted to the vehicle speed andtherefore it is difficult to efficiently operate the motor/generator andreduce capacity.

In particular, when the vehicle speed is increased and thus the rotationspeed of the motor/generator restricted to the vehicle speed isincreased, the efficiency of the motor/generator is reduced and thus theoptimal fuel efficiency may not be achieved.

Under this condition, when all of the engine ENG and the twomotors/generators MG1 and MG2 may control the rotation speed independentof the vehicle speed by coupling the first planetary gear set PG1connected to the engine ENG with two different rotation elements of thesecond planetary gear set PG2 connected to the output gear OG, thecontinuously variable transmission function is operated once again topromote the enhancement of fuel efficiency.

Therefore, when the second clutch CL2 is operated, the speed and torqueof the second motor/generator MG2 are restricted to the speed and torqueof the engine ENG by the third planetary gear set PG3 and the firstplanetary gear set PG1 and the second planetary gear set PG2 areconnected to each other by the second rotation shaft TM2, such that thespeed and the torque may be restricted to each other.

Further, the first and second motors/generators MG1 and MG2 need to havemutual electrical energy balance and all the rotation elements of thefirst and second planetary gear sets PG1 and PG2 perform an electricallycontrolled continuously variable transmission function while havinginterrelationship with the speed and the torque.

[ENG Mode 1]

A core technology to enhance the fuel efficiency of the hybrid electricvehicle may be said to be a recovery and reuse of braking energy and afree control of an operation point of the engine.

Further, to control the operation point of the engine, twice energyconversion processes of a process of converting the mechanical energy ofthe engine into the electrical energy in the motor/generator and aprocess of converting the electrical energy of the motor/generator intothe mechanical energy in the motor/generator again are involved.

The energy conversion causes a loss in the middle of the conversionprocesses without outputting all energy and under any driving condition,the fuel efficiency may be excellent in the ENG mode driven only by theengine rather than in the hybrid driving mode.

That is, in the ENG mode 1, when the first brake BK1 and the firstclutch CL1 are engaged with each other and the power of the engine ENGis transferred to the output gear OG through the second rotation shaftTM2. In this case, since the power of the first and secondmotors/generators MG1 and MG2 are not required, the vehicle is driven byonly the power of the engine and since the planetary gear sets are ruledout from the power transfer path, high power transfer efficiencycharacteristic appears.

[ENG Mode 2]

In the ENG mode 2, when the first clutch CL1 is engaged with the secondclutch CL2, all the rotation elements of the second planetary gear setPG2 integrally rotate and the power of the engine ENG is transferred tothe output gear OG through the third planetary gear set PG3 andtherefore a shift ratio is established as much as the gear ratio of thethird planetary gear set PG3.

As described above, according to the first exemplary embodiment of thepresent invention, in the overall configuration, the two EV modes, thethree HEV modes, and the two ENG modes may be implemented by thecombination of the three planetary gear sets PG1, PG2, and PG3, thethree friction elements BK1, CL1, and CL2, and the two motors/generatorsMG1 and MG2.

Further, according to the first exemplary embodiment of the presentinvention, the power of the engine ENG is input to the first ring gearR1 of the first planetary gear set PG1 and the power of the firstmotor/generator MG1 is input to the first sun gear S1 to transfer alarger torque than the engine ENG torque to the output shaft OS, therebyincreasing the usage of the mechanical power transfer path and using thelarger power of the engine than the specification of the same firstmotor/generator MG1.

Further, according to the first exemplary embodiment of the presentinvention, the larger torque than the engine torque may be transferredto the output shaft to implement the high rotation operation with thelarge power of the engine at the same vehicle speed at the time of theWOT oscillation and obtain the larger acceleration.

Further, according to the first exemplary embodiment of the presentinvention, since the larger acceleration in the HEV mode than in the ENGmode may be obtained, a necessity of conversion into the ENG mode at thetime of the oscillation is removed to configure a relatively simplersystem and reduce the friction element depending on the mode reduction,thereby more increasing the efficiency.

Further, it is possible to perform the driving without the electricalload of the first and second motors/generators by providing the ENG modeat the time of the high-speed driving, thereby improving the fuelefficiency.

FIG. 3 is a configuration diagram of a power transmission systemaccording to a second exemplary embodiment of the present invention.

Referring to FIG. 3, according to the first exemplary embodiment of thepresent invention, the first clutch CL1 which is the direct connectiondevice of the second planetary gear set PG2 is disposed between thefourth rotation shaft TM4 and the fifth rotation shaft TM5 but accordingto the second exemplary embodiment of the present invention, the firstclutch CL1 which is the direct connection device of the second planetarygear set PG2 is disposed between the second rotation shaft TM2 and thefifth rotation shaft TM5.

Compared with the first exemplary embodiment of the present invention,in the case of the second exemplary embodiment of the present invention,only the disposition positions of the first clutch CL1 are different andthe operation effect thereof is the same, and therefore the detaileddescription thereof will be omitted.

FIG. 4 is a configuration diagram of a power transmission systemaccording to a third exemplary embodiment of the present invention.

Referring to FIG. 4, according to the first exemplary embodiment of thepresent invention, the first clutch CL1 which is the direct connectiondevice of the second planetary gear set PG2 is disposed between thefourth rotation shaft TM4 and the fifth rotation shaft TM5 but accordingto the third exemplary embodiment of the present invention, the firstclutch CL1 which is the direct connection device of the second planetarygear set PG2 is disposed between the second rotation shaft TM2 and thefourth rotation shaft TM4.

Compared with the first exemplary embodiment of the present invention,in the case of the third exemplary embodiment of the present invention,only the disposition position of the first clutch CL1 is different andthe operation effect thereof is the same, and therefore the detaileddescription thereof will be omitted.

FIG. 5 is a configuration diagram of a power transmission systemaccording to a fourth exemplary embodiment of the present invention.

Referring to FIG. 5, according to the first exemplary embodiment of thepresent invention, the first planetary gear set PG1 is configured of thesingle pinion planetary gear set but according to the fourth exemplaryembodiment of the present invention, the first planetary gear set PG1 isconfigured of the double pinion planetary gear set.

Therefore, the first rotation shaft TM1 associated with the firstplanetary gear set PG1 is configured of the first sun gear S1, thesecond rotation shaft TM2 is configured to include the first ring gearR1 to the second planetary carrier PC2, and the third rotation shaft TM3is configured to include the first planetary carrier PC1.

Compared with the first exemplary embodiment of the present invention,in the case of the fourth exemplary embodiment of the present invention,only the configurations of the second and third rotation shafts TM2 andTM3 are different and the operation effects thereof are the same, andtherefore the detailed description thereof will be omitted.

FIG. 6 is a configuration diagram of a power transmission systemaccording to a fifth exemplary embodiment of the present invention.

Referring to FIG. 6, according to the first exemplary embodiment of thepresent invention, the second planetary gear set PG2 is configured ofthe single pinion planetary gear set but according to the fifthexemplary embodiment of the present invention, the second planetary gearset PG2 is configured of the double pinion planetary gear set.

Therefore, the second rotation shaft TM2 associated with the secondplanetary gear set PG2 is configured to include the first planetarycarrier PC1 and the second ring gear R2, the fourth rotation shaft TM4is configured to include the second sun gear S2 and the third ring gearR3, and the fifth rotation shaft TM5 is configured to include the secondplanetary carrier PC2.

Compared with the first exemplary embodiment of the present invention,in the case of the fifth exemplary embodiment of the present invention,only the configurations of the second and fifth rotation shafts TM2 andTM5 are different and the operation effects thereof are the same, andtherefore the detailed description thereof will be omitted.

FIG. 7 is a configuration diagram of a power transmission systemaccording to a sixth exemplary embodiment of the present invention.

Referring to FIG. 7, according to the first exemplary embodiment of thepresent invention, the third planetary gear set PG3 is configured of thesingle pinion planetary gear set but according to the sixth exemplaryembodiment of the present invention, the third planetary gear set PG3 isconfigured of the double pinion planetary gear set.

Therefore, the fourth rotation shaft TM4 associated with the thirdplanetary gear set PG3 is configured to include the second sun gear S2and the third planetary carrier PC3, the sixth rotation shaft TM6 isconfigured to include the third sun gear S3, and the seventh rotationshaft TM7 is configured to include the third ring gear R3.

Compared with the first exemplary embodiment of the present invention,in the case of the fifth exemplary embodiment of the present invention,only the configurations of the fifth and seventh rotation shafts TM5 andTM7 are different and the operation effects thereof are the same, andtherefore the detailed description thereof will be omitted.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner” and “outer” are used todescribe features of the exemplary embodiments with reference to thepositions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A power transmission system of a hybrid electricvehicle, comprising: an input shaft input with power of an engine; anoutput gear disposed on the input shaft without rotation interference; afirst planetary gear set disposed on the input shaft while includingthree rotation elements having a first sun gear, a first planetarycarrier, and a first ring gear; a second planetary gear set disposed ona same shaft line as the first planetary gear set while including threerotation elements having a second sun gear, a second planetary carrier,and a second ring gear; a third planetary gear set disposed on a sameshaft line as the second planetary gear set while including threerotation elements having a third sun gear, a third planetary carrier,and a third ring gear; a first rotation shaft directly connected to afirst motor generator as one of the rotation elements of the firstplanetary gear set; a second rotation shaft directly connected to theoutput gear while directly connecting one of the rotation elements ofthe first planetary gear set ruled out from the rotation elementsconfiguring the first rotation shaft to one of the rotation elements ofthe second planetary gear set; a third rotation shaft directly connectedto the input shaft as one of the rotation elements of the firstplanetary gear set ruled out from the rotation elements configuring thefirst and second rotation shafts; a fourth rotation shaft directlyconnected to a second motor generator while directly connecting one ofthe rotation elements of the second planetary gear set ruled out fromthe rotation elements configuring the second rotation shaft to one ofthe rotation elements of the third planetary gear set; a fifth rotationshaft selectively connected to a transmission housing as one of therotation elements of the second planetary gear set ruled out from therotation elements configuring the second and fourth rotation shafts; asixth rotation shaft continuously connected to the transmission housingas one of the rotation elements of the third planetary gear set ruledout from the rotation elements configuring the fourth rotation shaft; aseventh rotation shaft selectively connected to the third rotation shaftas one of the rotation elements of the third planetary gear set ruledout from the rotation elements configuring the fourth and sixth rotationshafts; and three friction elements configured to selectively connectthe respective rotation shafts to each other or selectively connect therespective rotation shafts to the transmission housing.
 2. The powertransmission system of claim 1, wherein all of the first, second, andthird planetary gear sets are a single pinion planetary gear set andinclude the first rotation shaft configured to include the first sungear and to be directly connected to the first motor generator; thesecond rotation shaft configured to include the first planetary carrierand the second planetary carrier which are directly connected to eachother and to be directly connected to the output gear; the thirdrotation shaft configured to include the first ring gear and to bedirectly connected to the input shaft; the fourth rotation shaftconfigured to include the second sun gear and the third ring gear whichare directly connected to each other and to be directly connected to thesecond motor generator; the fifth rotation shaft configured to includethe second ring gear and to be selectively connected to the fourthrotation shaft or the transmission housing; the sixth rotation shaftconfigured to include the third sun gear and to be directly connected tothe transmission housing; and the seventh rotation shaft configured toinclude the third planetary carrier and to be selectively connected tothe third rotation shaft.
 3. The power transmission system of claim 1,wherein the three friction elements include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the fourthrotation shaft to the fifth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 4. The power transmission system of claim 1,wherein the three friction elements include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the secondrotation shaft to the fifth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 5. The power transmission system of claim 1,wherein the three friction elements include a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the secondrotation shaft to the fourth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 6. The power transmission system of claim 1,wherein the first planetary gear set is a double pinion planetary gearset and the second and third planetary gear sets are a single pinionplanetary gear set and the first, second, and third planetary gear setsinclude the first rotation shaft configured to include the first sungear and to be directly connected to the first motor generator; thesecond rotation shaft configured to include the first ring gear and thesecond planetary carrier which are directly connected to each other andto be directly connected to the output gear; the third rotation shaftconfigured to include the first planetary carrier and to be directlyconnected to the input shaft; the fourth rotation shaft configured toinclude the second sun gear and the third ring gear which are directlyconnected to each other and to be directly connected to the second motorgenerator; the fifth rotation shaft configured to include the secondring gear and to be selectively connected to the second rotation shaftor the transmission housing; the sixth rotation shaft configured toinclude the third sun gear and to be directly connected to thetransmission housing; and the seventh rotation shaft configured toinclude the third planetary carrier and to be selectively connected tothe third rotation shaft.
 7. The power transmission system of claim 1,wherein the first and third planetary gear sets are a single pinionplanetary gear set and the second planetary gear set is a double pinionplanetary gear set and the first, second, and third planetary gear setsinclude the first rotation shaft configured to include the first sungear and to be directly connected to the first motor generator; thesecond rotation shaft configured to include the first planetary carrierand the second ring gear which are directly connected to each other andto be directly connected to the output gear; the third rotation shaftconfigured to include the first ring gear and to be directly connectedto the input shaft; the fourth rotation shaft configured to include thesecond sun gear and the third ring gear which are directly connected toeach other and to be directly connected to the second motor generator;the fifth rotation shaft configured to include the second planetarycarrier and to be selectively connected to the fourth rotation shaft orthe transmission housing; the sixth rotation shaft configured to includethe third sun gear and to be directly connected to the transmissionhousing; and the seventh rotation shaft configured to include the thirdplanetary carrier and to be selectively connected to the third rotationshaft.
 8. The power transmission system of claim 1, wherein the firstand second planetary gear sets are a single pinion planetary gear setand the third planetary gear set is a double pinion planetary gear setand the first, second, and third planetary gear sets include the firstrotation shaft configured to include the first sun gear and to bedirectly connected to the first motor generator; the second rotationshaft configured to include the first planetary carrier and the secondplanetary carrier which are directly connected to each other and to bedirectly connected to the output gear; the third rotation shaftconfigured to include the first ring gear and to be directly connectedto the input shaft; the fourth rotation shaft configured to include thesecond sun gear and the third planetary carrier which are directlyconnected to each other and to be directly connected to the second motorgenerator; the fifth rotation shaft configured to include the secondring gear and to be selectively connected to the second rotation shaftor the transmission housing; the sixth rotation shaft configured toinclude the third sun gear and to be directly connected to thetransmission housing; and the seventh rotation shaft configured toinclude the third ring gear and to be selectively connected to the thirdrotation shaft.
 9. A power transmission system of a hybrid electricvehicle, comprising: an input shaft input with power of an engine; anoutput gear disposed on the input shaft without rotation interference; afirst planetary gear set being a single pinion planetary gear set anddisposed on the input shaft while including three rotation elementshaving a first sun gear, a first planetary carrier, and a first ringgear; a second planetary gear set being the single pinion planetary gearset and disposed on a same shaft line at a rear side of the firstplanetary gear set while including three rotation elements having asecond sun gear, a second planetary carrier, and a second ring gear; athird planetary gear set being the single pinion planetary gear set anddisposed on a same shaft line at a rear side of the second planetarygear set while including three rotation elements having a third sungear, a third planetary carrier, and a third ring gear; a first rotationshaft configured to include the first sun gear and to be directlyconnected to a first motor generator; a second rotation shaft configuredto include the first planetary carrier and the second planetary carrierwhich are directly connected to each other and to be directly connectedto the output gear; a third rotation shaft configured to include thefirst ring gear and to be directly connected to the input shaft; afourth rotation shaft configured to include the second sun gear and thethird ring gear which are directly connected to each other and to bedirectly connected to a second motor generator; a fifth rotation shaftconfigured to include the second ring gear and to be selectivelyconnected to the fourth rotation shaft or a transmission housing; asixth rotation shaft configured to include the third sun gear and to bedirectly connected to the transmission housing; a seventh rotation shaftconfigured to include the third planetary carrier and to be selectivelyconnected to the third rotation shaft; and three friction elementsconfigured to selectively connect the respective rotation shafts to eachother or selectively connect the respective rotation shafts to thetransmission housing.
 10. The power transmission system of claim 9,wherein the three friction elements include: a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the fourthrotation shaft to the fifth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 11. The power transmission system of claim 9,wherein the three friction elements include: a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the secondrotation shaft to the fifth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 12. The power transmission system of claim 9,wherein the three friction elements include: a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch a direct connection device of the secondplanetary gear set and configured to selectively connect the secondrotation shaft to the fourth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.
 13. A power transmission system of a hybridelectric vehicle, comprising: an input shaft input with power of anengine; an output gear disposed on the input shaft without rotationinterference; a first planetary gear set being a double pinion planetarygear set and disposed on the input shaft while including three rotationelements having a first sun gear, a first planetary carrier, and a firstring gear; a second planetary gear set being a single pinion planetarygear set and disposed on a same shaft line at a rear side of the firstplanetary gear set while including three rotation elements having asecond sun gear, a second planetary carrier, and a second ring gear; athird planetary gear set being the single pinion planetary gear set anddisposed on a same shaft line at a rear side of the second planetarygear set while including three rotation elements having a third sungear, a third planetary carrier, and a third ring gear; a first rotationshaft configured to include the first sun gear and to be directlyconnected to a first motor generator; a second rotation shaft configuredto include the first ring gear and the second planetary carrier whichare directly connected to each other and to be directly connected to theoutput gear; a third rotation shaft configured to include the firstplanetary carrier and to be directly connected to the input shaft; afourth rotation shaft configured to include the second sun gear and thethird ring gear which are directly connected to each other and to bedirectly connected to a second motor generator; a fifth rotation shaftconfigured to include the second ring gear and to be selectivelyconnected to the second rotation shaft or the transmission housing; asixth rotation shaft configured to include the third sun gear and to bedirectly connected to the transmission housing; a seventh rotation shaftconfigured to include the third planetary carrier and to be selectivelyconnected to the third rotation shaft; and three friction elementsconfigured to selectively connect the respective rotation shafts to eachother or selectively connect the respective rotation shafts to thetransmission housing.
 14. The power transmission system of claim 13,wherein the three friction elements include: a first brake configured toselectively connect the fifth rotation shaft to the transmissionhousing; a first clutch being a direct connection device of the secondplanetary gear set and configured to selectively connect the secondrotation shaft to the fifth rotation shaft; and a second clutchconfigured to selectively connect the third rotation shaft to theseventh rotation shaft.